As illustrated in FIG. 20, the steering apparatus of an automobile is constructed such that it applies a steering angle to the front wheels by transmitting the rotation of a steering wheel 1 to an input shaft 3 of a steering gear unit 2, and pushing or pulling a pair of left and right tie rods 4 as the input shaft 3 rotates. The steering wheel 1 is supported by and fastened to the rear end section of a steering shaft 5, and with the steering shaft 5 passed in the axial direction through a cylindrical shaped steering column 6, the steering shaft 5 is supported such that it can rotate freely. The front end section of the steering shaft 5 is connected to the rear end section of an intermediate shaft 8 via a universal joint 7, and the front end section of the intermediate shaft 8 is connected to the input shaft 3 via a separate universal joint 9.
During a collision accident, after a primary collision of an automobile with another automobile, a secondary collision occurs in which the body of the driver hits the steering wheel. Therefore, in order to protect the driver, it is necessary for this kind of steering apparatus for an automobile to have construction such that impact energy will be absorbed during a collision accident while the steering wheel displaces in the forward direction. As this kind of construction, patent literature 1 to 5 disclose construction in which the steering column that supports the steering wheel is supported with respect to the vehicle body such that it is capable of collapsing forward due to an impact load in the forward direction during a secondary collision, and an energy absorbing member that absorbs the impact load by plastically deforming is provided between the vehicle body and a member that displaces forward together with this steering column, with such construction already being widely used.
FIGS. 21 to 24 illustrate an example of the construction of an automobile steering apparatus that comprises this kind of impact absorbing function. This construction comprises a tilting mechanism for adjusting the vertical position of the steering wheel 1 (FIG. 20), and a telescoping mechanism for adjusting the forward/backward position thereof, and further comprises a steering column 6a, a support bracket 10, a pair of left and right held wall sections 11 that are provided on the steering column 6a side, and a bracket 12 on the vehicle body side. Of these, the steering column 6a is constructed such that the entire length can extend or contract by fitting together the front section of an outer column 13 on the rear side with the rear section of a inner column 14 on the front side such that they can displace relative to each other in the axial direction. A steering shaft 5a is supported on the inner-diameter side of this kind of steering column 6a such that it can rotate freely. This steering shaft 5a is also constructed such that it can extend or contract along the entire length by combining together an outer shaft and an inner shaft.
A housing 16 for installing component parts of an electric-powered steering apparatus such as an electric motor 15 (FIG. 20) and reduction gear is connected and fastened to the front end section of the steering column 6a. This housing 16 is supported by part of the vehicle body by a bolt (not illustrated in the figure) that is inserted through a support pipe 17 that is provided in the width direction at the top of the housing such that the housing can pivot. The steering wheel 1 is fastened to the rear end section of the steering shaft 5a in the portion that extends further to the rear than the steering column 6a. Moreover, the portion of the front end section of the steering shaft 5a that protrudes further forward than the steering column 6a is connected to an intermediate shaft 8 (FIG. 20) by way of a universal joint 7. Here, the width direction is the width direction of the vehicle when the steering apparatus is assembled in the vehicle.
The support bracket 10 is connected to and supported by the bracket 12 on the vehicle body side, such that it can displace in the forward direction and break away when being subjected to the impact load due to a secondary collision. The support bracket 10 is made of a metal plate such as steel plate having sufficient strength and rigidity, and is formed by connecting and fastening together a top plate 18 and a pair of side plates 19a, 19b by welding or the like. Of these, both end sections in the width direction of the top plate 18 function as connection plate sections 20 for supporting and connecting the support bracket 10 to the bracket 12 on the vehicle side. As illustrated in FIG. 24, cut out sections 21 that open up the edge on the rear end of the connection plate sections 20 are formed in the center section in the width direction of these connection plate sections 20, and capsules 22 are mounted in each of these cut out sections 21.
These capsules 22 axe made of a material that slides easily over the metal plate of the top plate 18 such as synthetic resin or a light alloy including an aluminum alloy. In the normal state, these capsules 22 do not come out from the cut out sections 21, however, when a large impact load is applied in the forward direction to the support bracket 10, members that lock the support bracket 10 inside the cut out sections 21, for example, support pins that span between the top plate 18 and these capsules 22 shear off and the capsules come out of the cut out sections 21 toward the rear. Through holes 23 through which bolts or studs are passed for supporting and connecting the support bracket 10 to the bracket 12 on the vehicle side are provided in the center section of each of these capsules 22. In order to support and connect the support bracket 10 to the bracket 12 on the vehicle side, a bolt is inserted from bottom to top through the through holes 23 of the capsules 22 and screwed into a nut 24 that is supported by and fastened to the bracket 12 on the vehicle side by welding or the like, and tightened. This bracket 12 on the vehicle side is fastened to the vehicle side beforehand, so by tightening the bolt, the support bracket 10 is fastened to and supported by the vehicle body such that it can collapse forward only when a large impact load is applied in the forward direction. The support bracket 10 can also be connected to and supported by the bracket 12 on the vehicle side by inserting a stud that is fastened to the bottom surface of the bracket 12 on the vehicle side from top to bottom through the through hole 23 in the capsule 22 and screwing the bottom end section of this stud to a nut and tightening.
In a pair of holding plate sections 25a, 25b of the side plates 19a, 19b which sandwich the outer column 13 from the both side, long holes 26 are formed at portions that are aligned with each other. These long holes 26 in the vertical direction are formed into a partial circular arc shape around the center axis of the support pipe 17 as the center. The outer column 13 is supported between the side plates 19a, 19b by a tightening rod 27 that is inserted through these long vertical holes 26. In order for this, held wall sections 11 are formed on the upper part of the front section of the outer column 13, and long holes 28 in the forward/backward direction are formed in these held wall sections in the axial direction of the outer column 13 (FIG. 4 and FIG. 6). The outer column 13 is supported by the support bracket 10 by way of the tightening rod 27 that is inserted through the long holes 26 in the vertical direction and the long holes 28 in the forward/backward direction. Therefore, the outer column 13 can pivot in the up or down direction around a bolt that is inserted through the support pipe 17 within the range that the tightening rod 27 can be displaced inside the vertical long holes 26. The outer column 13 can also displace forward and backward (axial direction) within the range that the tightening rod 27 can be displaced inside the long holes 28 in the forward/backward direction.
An outward facing flange shaped rim section 29 is fastened to one end section (right end section in FIG. 22) of the tightening rod 27, and a cam unit 32 having a drive cam 30 and a driven cam 31 is provided on the other end section. By using an adjustment lever 33 to rotate and drive the drive cam 30, it is possible to increase or decrease the distance between the driven cam 31 and the rim section 29. By rotating the adjustment lever 33 in the downward direction when adjusting the position of the steering wheel 1, the distance between the driven cam 31 and the rim section 29 is increased, and in this state, the outer column 13 is displaced within the range that the tightening rod 27 can be displaced inside the long holes 26 in the vertical direction and inside the long holes 28 in the forward/backward direction. This adjusts the position of the steering wheel 1, which is supported by and fastened to the rear end section of the steering wheel shaft 5a that is supported inside this outer column 13 such that it rotates freely. The weight of the portion that raises and lowers together with the outer column 13 is supported by an equalizer spring 35 that is provided between the tightening rod 27 and a locking section 34 that is provided in the support bracket 10. Therefore, it is not necessary for the driver to carry the entire weight of these when adjusting the position of the steering wheel 1.
After the position of the steering wheel 1 has been adjusted, by rotating the adjustment lever 33 upward, the distance between the driven cam 31 and the rim section 29 is decreased. As a result, the inside surfaces of the holding plate sections 25a, 25b strongly come in contact against the outside surfaces of the held wall sections 11, and due to the frictional engagement between these surfaces, the steering wheel 1 is fastened in a vertical position. Moreover, the outer diameter of the front end section of the outer column 13 where the held wall sections 11 are located is decreased, the inner circumferential surface of the front end section of the outer column 13 comes in strong contact with the outer circumferential surface of the rear end section of the inner column 14, and due to the frictional engagement between these surfaces, the steering column 6a is unable to extend or contract. As a result, the front and rear positions of the steering wheel 1 are fastened.
In an automobile steering apparatus having this kind of construction, when a secondary collision occurs after a collision accident, the capsules 22 remain as they are on the side of the bracket 12 on the vehicle body side, while the support bracket 10 displaces in the forward direction. In other words, a large impact load in the forward direction that occurs due to a secondary collision is applied to this support bracket 10 from the steering wheel 1 via the steering shaft 5a, outer column 13 and tightening rod 27. The members that lock the capsules in the connection plate sections 20 shear off, and as these capsules 22 come out from the cut out sections 21, the support bracket 10 displaces in the forward direction. As a result, the steering wheel 1 also displaces in the forward direction, which makes it possible to lessen the impact that is applied to the body of the driver that hits against this steering wheel 1.
When the steering wheel 1 displaces in the forward direction in this way due to a secondary collision, preferably, from the aspect of protecting the driver, the impact energy that is applied to the steering wheel 1 from the body of the driver is absorbed, and the steering wheel is caused to displace in the forward direction. For example, in the construction illustrated in FIG. 21 to FIG. 24, friction force that acts on the contact area between the outside surfaces of the held wall sections 11 and the inside surfaces of the holding plate sections 25a, 25b, and the friction force that acts on the contact area between the inner circumferential surface of the front section of the outer column 13 and the outer circumferential surface of the rear section of the inner column 14 become resistance to the displacement of the steering wheel 1 in the forward direction, and contributes to absorbing the impact energy. However, the ability for the friction force to absorb energy is unstable, and so that alone makes it difficult to completely protect the driver.
In regards to this, patent literature 2 discloses construction in which an energy absorbing member is provided between the vehicle body and the steering column that displaces in the forward direction during a secondary collision. In this construction, as illustrated in FIG. 25 and FIG. 26, an energy absorbing member 36, which is formed by bending a plastically deformable wire rod, is located between a support pin 38 that is fixed to the upper surface of the steering column 6b and a support casing 39 that is fastened to the vehicle body. When the steering column 6b displaces in the forward direction due to a secondary collision, the energy absorbing member 36 elongates from the state illustrated in FIG. 26A to the state illustrated in FIG. 26B. The energy required for this elongation is absorbed from the impact energy that is applied to the steering wheel from the driver's body, which lessens the impact that is applied to the driver's body.
An impact absorbing structure that uses this kind of energy absorbing member 36 can be assembled in the impact absorbing steering apparatus illustrated in FIG. 21 to FIG. 24, making it possible to improve the energy absorption capability, however, in order to obtain better performance at low cost while maintaining the freedom of design, improvements are desired according to the points below.
First, it is desired that the moment in the pivot direction that is applied to the outer column 13 of the steering column 6a during a secondary collision be reduced or eliminated. In other words, when the construction illustrated in FIG. 25 and FIG. 26 is incorporated in a steering apparatus, regardless of whether or not there is a steering wheel position adjustment device such as a tilt mechanism or telescoping mechanism, the installation position of the energy absorbing member 36 and the tightening rod 27 (FIG. 22) may be at right angles with respect to the center axis of the outer column 13. When there is this kind of offset, a moment in the pivot direction occurs during a secondary collision. In other words, the energy absorbing member 36 functions as a resistance to displacement in the forward direction of the outer column 13 during a secondary collision. As a result, a moment is applied to the steering column 13 with the tightening rod 27 as the pivot point and the energy absorbing member 36 as the input. Therefore, as the secondary collision proceeds, the friction state in the engagement between the outer circumferential surface of the front section of the outer column 13 and the inner circumferential surface of the rear section of the inner column 14 becomes unstable, and thus the energy absorption performance in this engagement section becomes unstable.
This kind of instability in the energy absorption performance can be reduced or eliminated by placing both the energy absorbing member 36 and tightening rod 27 on the same side in the vertical direction of the steering column 6a, 6b, and by reducing the offset in the orthogonal direction with respect to the center axis of the steering column 6a, 6b that exists between these members 36, 27. However, the tightening rod 27 is often located on the lower side of the steering column 6a, 6b. In this case, as illustrated in FIG. 25 and FIG. 26, construction is such that the energy absorbing member 36 is located between the steering column 6b and the vehicle body 37 located on the upper side of this steering column 6b, so it is not possible to reduce the momentum, and thus it is not possible to prevent the energy absorption performance from becoming unstable. In other words, in the construction illustrated in FIG. 25 and FIG. 26, when there is an intention to keep the moment small and prevent the energy absorption performance from becoming unstable, construction in which the tightening rod 27 is located on the lower side of the steering column cannot be employed, and freedom of design is limited. Moreover, in the construction illustrated in FIG. 25 and FIG. 26, the support pin 38 and support casing 39 become necessary as special part for installing the energy absorbing member 36, so an increase in cost in unavoidable.